Sensors are used in myriad systems and environments to sense numerous and varied physical phenomena. In some instances, sensors are disposed in potentially hazardous environments. As used herein, a potentially hazardous environment is one in which, though unlikely, it is postulated that, because flammable gases or other combustible material may be present, the potential for a conflagration may be increased. Thus, sensors that are disposed in hazardous environments need to meet relatively strict safety requirements. These requirements can be met by following generally well-known protection protocols, such as explosion-proofing, increased safety, and intrinsic safety.
A sensor meets the intrinsic safety protocol when it is incapable of generating a spark or other thermal effect that can ignite a flammable or combustible material or mixture. When such sensors, sometimes referred to as “intrinsically safe sensors”, are connected to non-intrinsically safe equipment or devices that are located in non-hazardous areas, safety barrier devices are used. These devices limit the electrical energy (e.g., voltage, current, power) supplied to the sensor(s) disposed in the hazardous area to predetermined values, generally referred to as “entity parameters.” For example, when a 4-20 milliamp (mA) loop powered sensor that meets the intrinsically safe protocol is used, safety barrier devices limit the entity parameters to less than 28V and 110 mA.
Some intrinsically safe 4-20 mA sensors are configured to allow bidirectional digital communication via a 1-wire UART interface. However, when safety barrier devices are used in conjunction with these sensors to meet the desired entity parameters, the 1-wire UART bidirectional digital communication is not supported.
Hence, there is a need for a means of supporting 1-wire UART bidirectional digital communication for intrinsically safe 4-20 mA sensors when connected to a safety barrier device. The present invention addresses at least this need.